The present invention relates to a process for preparing bisphenol alkoxylates, in particular bisphenol A alkoxylates. In addition the invention relates to the use of catalysts employed for this purpose.
Bisphenol alkoxylates are used for a wide variety of applications, for example for the synthesis of polyester resins (JP 59012-934-A) and polyurethanes (JP 59197-417-A).
Bisphenol alkoxylates, in particular bisphenol A alkoxylates, are prepared, as is known to those skilled in the art, from bisphenol A by reaction with an alkylene oxide, e.g. ethylene oxide, propylene oxide or butylene oxide (JP 60243-036-A), in the presence of a catalyst. Catalysts used are, in particular, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide or tertiary amines (see the above mentioned JP publications and also Shanghai Inst. Chem. Technol., Shanghai in Chemical Abstracts 94:48110).
The alkoxylation reaction can lead to different addition products. The known catalysts, for instance, lead to a product in which the addition products have a relatively broad molar mass distribution.
If a high reaction selectivity is desired, solvents are sometimes used in order to influence the selectivity of the alkylene oxide addition onto bisphenol A in the desired direction (U.S. Pat. No. 4,846,996). However, this measure leads to a reduction in the space-time yield, since the solvent used has to be removed again after the reaction is complete.
Another possible way of solving the problem is to allow the reaction of a phenol with an alkylene oxide to proceed in the presence of phosphonium halides as catalysts, in the presence or absence of a solvent.(JP AS 654/75; DE-A 2 157 455).
A further measure to obtain a bisphenol A addition product having a narrow molar mass distribution is crystallization of the product. However, this step likewise reduces the space-time yield and additionally leads to reduced yields.
Sheng Zhicong et al. [Shang-hai Hua Kung Hsueh Yuan Hsueh Pao 1980, 48 (1), 92] describe studies on the reaction of propylene oxide with bisphenol A. It is stated that the preferred catalyst is NaOH and that the amount of catalyst can be reduced if concomitant use is made of a Lewis base such as triethylamine or triphenylphosphine (i.e. the Lewis base is used as cocatalyst). However, further information which would enable a person skilled in the art to carry out the reaction is lacking in this publication. In addition, there is the undesirable effect that the catalyst loses its activity toward the end of the reaction and the bisphenol A monopropoxylate content is increased as a consequence.
A low selectivity is therefore to be expected when using other alkylene oxides, too. This applies especially to ethylene oxide, since ethylene oxide is significantly more reactive than propylene oxide. A person skilled in the art would therefore expect the formation of multiply ethoxylated products and thus a broader molar mass distribution.
It is an object of the present invention to provide a process for preparing bisphenol alkoxylates, in particular bisphenol A alkoxylates, which gives, dialkoxylated products with high selectivity and in which, in particular, uncontrolled multiple alkoxylation is avoided.
We have found that this object is achieved by a process for preparing bisphenol alkoxylates, which comprises reacting at least one bisphenol with an alkylene oxide in the presence of a phosphine catalyst.
In a preferred embodiment, the process of the invention is carried out in the absence of solvents, i.e. a mixture, in particular a melt, of the bisphenol and the phosphine catalyst is prepared first and the reaction with the alkylene oxide is then carried out. However, the reaction can also be carried out in the presence of an inert solvent. Solvents which can be used are, for example, hydrocarbons such as toluene or xylene and ketones such as methyl ethyl ketone or diethyl ketone.
Preferred alkylene oxides are C2-C4-alkylene oxides, in particular ethylene oxide, propylene oxide and 1,2-butylene oxide and mixtures thereof, with particular preference being given to ethylene oxide. Styrene oxide is also suitable.
In the process of the present invention, the catalysts used are materials belonging to the class of substituted phosphines. These are preferably selected from the group consisting of substituted phosphines of the formula (I) below: 
where R1, R2 and R3 are aryl radicals of the formula (II) below, 
where R4 and/or R5 can be identical or different and are selected from among H, C1-C3-alkyl groups, C1-C3-alkoxy groups, carboxyl groups and sulfonic acid groups.
Preferred catalysts of the above formula (I) are phosphines in which at least two of the radicals R1, R2 and R3 are identical. Particular preference is given to phosphines in which the substituents R1, R2 and R3 are identical.
Very particular preference is given to substituted phosphines in which the radicals R1, R2, R3 are phenyl, o-tolyl, m-tolyl or p-tolyl groups. Such particularly preferred phosphine catalysts include, for example, tri-para-tolylphosphine, tri-ortho-tolylphosphine, tris(3-sulfophenyl)phosphine and its salts, in particular the trisodium salt, and particularly preferably triphenylphosphine.
The phosphine catalyst can also be employed together with a tri-C1-C12-alkylamine as cocatalyst. The amount of cocatalyst can be up to 35% by weight, based on the total weight of the catalyst. Examples of cocatalysts are triethylamine, tri-n-propylamine, tri-n-butylamine, etc.
The phosphine catalysts described are particularly suitable for the reaction of bisphenols of the formula 
where A is a straight-chain or branched C1-C4-alkylene group, 
xe2x80x94CH2OCH2xe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94. Preferably, A is 
The OH groups are preferably in the 4 and 4xe2x80x2 positions.
Particular preference is given to bisphenol A (2,2-bis(4-hydroxyphenyl)propane), bisphenol B (2,2-bis(4-hydroxyphenyl)butane), bisphenol C (1,4-bis(4-hydroxyphenyl)cyclohexane) and bisphenol F (2,2xe2x80x2-methylenediphenol).
The alkoxylation products obtained are thus bisphenol alkoxylates of the formula 
where A is as defined above, m and n are 0 or 1, with m and n being able to be identical or different but not both 0, and Alk is a C2-C4-alkylene group or C6H5xe2x80x94CHxe2x80x94CH2xe2x80x94, in particular xe2x80x94CH2-CH2xe2x80x94,
The process of the invention can be illustrated by means of scheme 1 below using the reaction of bisphenol A with ethylene oxide as an example. 
A very particular advantage of the process of the invention is the high reaction selectivity, in particular with avoidance of the use of a solvent.
The process of the invention is preferably carried out at from 90xc2x0 C. to 180xc2x0 C. The pressure is generally in the range from 1 to 50 bar, preferably from 1 to 20 bar, in particular from 2 to 15 bar.
The catalyst is generally used in an amount of from 0.01 to 5% by weight, preferably from 0.1 to 5% by weight, in particular from 0.1 to 2% by weight, based on bisphenol used. In general, the reaction is carried out essentially in the absence of water, i.e. the water content of the reaction mixture is xe2x89xa61% by weight, based on the weight of the reaction mixture.
The amount of alkylene oxide used depends on the product desired. In general, it is used in an amount of from about 1.9 to 2.5 equivalents, based on bisphenol. After the reaction is complete, the alkylene oxide is removed in a customary manner, e.g. by application of a vacuum.
In a preferred embodiment of the process of the present invention, the bisphenol dialkoxylates obtained in accordance with scheme 1 above are converted into the corresponding more highly alkoxylated bisphenol alkoxylates in a subsequent reaction with an alkylene oxide (ethylene oxide, propylene oxide, butylene oxide or styrene oxide). As catalyst, use is made here of an alkali metal hydroxide such as NaOH, KOH, CsOH or LiOH, an alkaline earth metal hydroxide such as magnesium hydroxide or calcium hydroxide or a DCM catalyst as described, for example, in WO 99/16775. The subsequent reaction is illustrated in scheme 2 below using KOH as catalyst and ethylene oxide: 
In this scheme, m and n can be identical or different and be from 0 to 20, in particular 0, 1, 2 or 3, with m and n not both being able to be 0. It has surprisingly been found that the more highly alkoxylated compounds can also be obtained in purer form than is obtained according to the prior art. Preference is given to syntheses which lead to compounds with m=n=1.
The above-described subsequent reaction is carried out under essentially the same conditions as the reaction of the bisphenol with the alkylene oxide.
Bisphenol ethoxylates which can be synthesized by means of the process of the present invention are shown below by way of example: 
The invention is illustrated by the following example.